P-057: GENETIC VARIABILITY AND DISEASE SEVERITY IN A COHORT OF ANGOLAN SICKLE CELL DISEASE PATIENTS
Authors: BRITO M., FERREIRA J., CAPRIELLO I., GINETE C., DELGADINHO M., SEBASTIÃO C., MENDES M., QUINTO F., MAVUNZA F., VASOONCELOS J., COGLE A.
Journal: HemaSphere (2022)

Purpose: Sickle Cell Anaemia (SCA) is an inherited autosomal and lethal blood disorder caused by a mutation in the HBB gene that promotes haemoglobin (Hb) polymerization and consequent sickling of red blood cells (RBCs) in hypoxia. Regardless of being a monogenic disease, SCA has a remarkably high clinical heterogeneity in its phenotypic expression. Several factors have been shown to modulate the clinical manifestations of SCA, namely genetic markers such as α-thalassaemia and β-globin cluster haplotypes, that can modulate biological parameters like the degree of haemolytic anaemia or the levels of foetal haemoglobin (HbF). Materials and methods: Our study incorporates 112 patients of all ages and genders that are followed in the SCA consultation at Clínica Girassol and obstetrics consultation at Maternidade Lucrécia Paim, in Luanda. All patients or their legal caretakers, in the case of minor patients, signed an informed consent form. Clinical, biochemical, and haematological data were collected, as well as the patient’s clinical history including the age at diagnosis, the number of hospitalizations, blood transfusions and strokes, among others Additionally, samples of peripherical blood were used for genetic analysis. All samples were genotyped for the HbS mutation by PCR-RFLP to confirm the SCA diagnosis. Moreover, four SNPs were genotyped in the β-cluster to determine the HbS haplotype by RT-PCR (rs968857, rs10128556) and PCR-RFLP (rs28440105, rs3834466). The presence of the 3.7kb deletion of the α-globin gene was determined by Gap-PCR Results: A total of 112 SCA patients, including 76 females (67,9%) and 32 males (28,6%), were studied with ages ranging from 1 to 67 years old (mean of 18,8±12,1). All the samples were homozygous for the HbS mutation. The observed frequency of homozygous for 3.7kb α-thalassaemia deletion was 14%, with an allelic frequency of 35% in this sample. The data was consistent with the Hardy-Weinberg equilibrium (χ2=0.823, p=0.364) with the wild-type homozygous genotype being 44% and the heterozygous genotype being 42%. Most of the patients have the CAR/CAR haplotype (86 patients, 76,8%), and all the patients have at least one CAR allele. We observed an apparent differential survival of SCA patients that co-inherit the α-thalassaemia deletion, and with the homozygous CAR haplotype. We observed apparent higher mortality for homozygous with the normal alpha gene and for heterozygous, as well as an increase in 3.7kb α-thalassaemia deletion frequency in the individuals above ten years old. This effect was more evident when comparing the under-10 and over-10 years classes. Moreover, a clear decrease in the frequency of CAR homozygotes was observed in older age classes. This differential survival should be taken into account during patient management since the first ages of diagnosis. Analysing the haematological data, we observed also that the presence of the α-thalassaemia deletion reflects on the red blood cell count (p-value < 0.001) and on the haemoglobin level (p-value = 0.029). Conclusion: We confirm the positive impact of co-inheritance of 3.7kb α-thalassaemia deletion in SCA patients, particularly in the clinical severity and survival. The genetic polymorphisms studied can be powerful prognostic markers. The authors do not declare any conflict of interest